256 
GASTEROPODA OF THE INFERIOR OOLITE. 
so obvious. D’Orbigny bad no difficulty in referring them all to the genus Natica. 
Whether there were traces of an umbilicus or not, whether the whorls were 
square-shouldered or round-shouldered, these differences were not accounted as of 
generic importance. Seeing, however, that the genus thus constituted would 
include very divergent forms, he divided it into four groups, of which the fourth 
group, viz. the Prdelongse, is characterised by the length of the shell exceeding 
the width. To this by far the larger portion of his Jurassic Naticx were 
assigned. 
Genus — Natica, Adanson, 1757 ; as defined by D’Orbigny, 1852. 
“ Shell globular, thiclc, varying from the depressed to the elongated form,. Spire 
usually short. Mouth oval or semilunar, modified by the ivinding of the spire . 
Umbilical region very variable, simple or compound, open or closed by callosities.'' 
Morris and Lycett, in dealing with the Naticidge of the Great Oolite, classed the 
round-shouldered forms for the most part under Natica, and the square-shouldered 
forms under a sub-genus — Eiispira (Ag.). The following is their diagnosis : 
Sub-genus — Buspira, Agassiz, 1837, as defined by Morris and Lycett, 1851. 
Shell smooth, ovate; spire elevated; of few ivhorls vjhich are angulated, the 
angles sometimes talcing the form of a carina^ .... aperture entire, elliptical, 
modified by the angle of the whorl ; base ivide, rounded ; pillar-lip smooth and 
excavated, outer lip thin and smooth." 
Mons. Cossmann, in his ^Contribution to the Fauna of the Bathonian in 
France,” like d’Orbigny, minimises the difference between the round-shouldered 
and the square-shouldered Naticidge, but groups the whole under the genus 
Ampullina, Lamarck. This is divided by Dr. Fischer (‘ Manual,’ p. 766) into 
sectioi :s and sub-genera, one of the latter being Euspira, which he thus describes : 
— “ Whorls swollen or canaliculate at the suture ; spire sometimes elevated, umbilical 
fissure but little indicated or concealed." 
There can be no doubt that most of the Naticidee of our Inferior Oolite might 
be classed under Euspira; but then we are met by this difficulty, that some of 
Lycett’s species, such as Euspira canaliculata, were classed by that author under 
Euspira, whilst others, such as Natica Oppelensis, were classed under Natica. And 
yet no shells can have a better title to be regarded as Euspira than Natica 
Oppelensis, Natica adducta, Natica Lorieri, &c. Moreover, the only species of 
Natica known to me in the Lias of this country, viz., Natica Pelops, D’Orb. 
{N. buccinoides, Y. & ~B.,fi,de Tate) must come under this designation. In the 
' The portion of the diagnosis framed for the admission of “ Muspira ” coronata is omitted. 
